Method and apparatus for producing alternating currents.



n. A. FESSENDEN. METHOD AND APPARATUS FOR PRODUCING ALTERNATING CURRENTS.

APPLICATION FILED DEC-Z. I914.

Patented May 7,1918.

FDR: W

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UNITED STATES PATENT OFFICE.

REGINALD AUTSREY FESSENDI EN, OF BROOKLINE, MASSACHUSETTS, ASSIGNOR TO SUBMARINE SIGNAL COMPANY, OF WATERVILLE, MAINE, A CORPORATION OF MAINE.

METHOD AND APPARATUS FOR PRODUCING- ALTEBNATIN G CUIBRENTS.

To all whom it may concern:

Be'it known that I, REGINALD A. FESSEN- DEN, of Brookline, in the county of Norfolk and State of Massachusetts, a citizen ofthe United States, have invented a new and Improved Method and Apparatus for Producing Alternating Currents, of which the following is a specification.

Heretofore alternatingcurrents have been produced by alternating current dynamos or by commutators in which a continuous current was broken and reversed in direction.

The former method requires special machinery so that even if there be 100 H. P. of direct current available, a 100 H. P. alternating current dynamo is also required.

The latter method would be much simpler and less expensive, but has the disadvantage that the breaking of the continuous current, owing to the self-induction of the circuit, produces very severe sparking at the contacts, which renders it for most purposes impracticable.

The invention herein described has for its object the production of alternating currents from direct currents in a simple, economical and efficient manner,-and has also for its object the production of a wave form adapted for special purposes. 4

' In the accompanying drawings forming a part of this specification, are. shown diagrammatically arrangements for carrying out my invention.

Figure 1 shows diagrammatically the primary circuit including a. continuous current generator and a secondary circuit compris-J mg a condenser and the means to be operated together with a pole changer.

Fig. 2 shows a modification more fully described below.

. Briefly stated, the invention consists in that instead of allowing a continuous current to establish itself in the circuit and then breaking it after it has established its magnetic field, with the consequent destructive s arking, and then allowing it to establish ltself in the opposite direction and breaking it again, a condenser is located in the circuit in which it is desired to create the alternating current, and the continuous current is connected to this condenser so as to 7 charge the condenser.

As soon as the condenser is charged the flow of current stops of itself and it is only Specification of Letters Patent.

Application filed December 2, 1914. Serial No. 875,071.

Patented May '7, 1918.

-then that the circuit is broken, there being I now no sparking, and the continuous current is then connected so as to charge the condenser in the opposite direction, and when it is charged in the opposite direction and the charging current has ceased to flow, the circuit is broken once more and so on In this way it is possible to produce alternating currents of large horse power from continuous currents, and without destructive sparking; in fact, in the apparatus constructed and used by the applicant, no sparkingdat all is visible when operating at full In the drawing illustrating the invention, 11 is a continuous current dynamo which may be of 110 volts; 12 is the positive lead and 13 the negative lead; 3, 4 and 5 are segments of a rotating commutator or other pole changer.

The segments 3,3, 3 are connected to each other and to the negative pole, and the segments 4,4, 4 are connected to each other and to thepositive pole. The segments 5, 5, 5, 5,

5, 5, '5 are insulated segments.

7 is a device which is to be operated by tor of the type described in applicants United States application for a patent, Serial N 0. 770,857, filed May 31, 1913, United States Patent No. 1,167,366.

6 is a condenser, and 15 and 16 are brushes.

It will be seen that when the brush l5 rests on the segment 3 and the brush 16 on the segment 4. the condenser 6 will be charged with its lower plate negative, and that while it is being charged there will be a rush of current in one direction through the oscillator circuit. When the charging is accomplished, the'commutator moving to the left, the brushes 15 andl6-will move ofi the segments 3 and 4, but no spark will be produced because as soon as the condenser 6 was charged the current flow sto ped ofitself.

aving moved of]? the segments 3 and 4 the brushes 15 and 16 move onto the segments 5 and 5 in which position they are insulated.

As the commutator continues to move to the left, the brush 15 makes contact with the segment 4 and the brush 16' with the segment 3, whereupon it will be seen that alternating current, for example, an oscilla the continuous current now flows on through the brushes and first annuls the charge left in the condenser 6 and then charges it in the opposite direction, so that by this reversal double the charging current is obtained and therefore double the alternating current to what would be obtained by a simple charge instead of a reversal of the charge.

In the apparatus actually constructed the commutator revolved about 1000 times per minute and the time taken by each segment in passing under the brush was about 1/2000 of a second. As is well-known in the art (see Bedcll, Alternating Currents), the time constant of a circuit is the time in which said circuit discharges itself nearly completely, and therefore, in order that a circuit may be discharged completely in a given interval of time the, time constant of the circuit must be substantially less than said interval of time.

The time-constant of the oscillator being l/10000 of a second, the condenser 6 was fully charged before the brushes had travveled more than one quarter of the way across a commutator bar, and consequently the current had entirely ceased to flow before the circuit was broken.

It will be obvious that if the time constant had been 1/1000 instead of 1/10000 the condenser would not have finished charging before the brush passed off the commutator bar and there would have been sparking, and that obviously to prevent this sparking the time constant should be half the frequency or less.

In order to prevent oscillatory charges of the condenser 6 the virtual resistance of the oscillator and its connections was made sufficient to damp out oscillatory discharges, though in some cases the oscillatory discharge was permitted to exist and the commutator rotated at such speed as to utilize the natural oscillations.

Fig. 2 shows another arrangement for utilizing the commutator in which 9 is the transformer, 8 being its primary, 10 its secondary, 6 a condenser in series with the primary and 17 and 18 brushes resting on the commutator. In this arrangement it is preferred to use a condenser 1a in the secondary of the transformer so as to reduce the time-constant of the transformer sufficiently to allow the condenser 6 to be charged substantially before the current is broken.

This apparatus the applicant has used in practice with very satisfactory results, a small commutator 6 in diameter and condenser-s occupying a cube of approximately 4!- on the side, having taken the place of a 2 K. W. 500 cycle motor generator set, formerly used with the oscillator.

l/Vhat I claim as my invention is 1. A method of producing alternating current from direct current which consists in first adjusting an electric current circuit containing a condenser so as to have a time constant less than one-half the period of the frequency desired, thereby enabling the condenser to be charged in less time than the time of one-half the period of the frequency desired, then connecting by means of a pole changer the adjusted electric current circuit to a source of con tinuous current thereb char in the conof said commutator, and an electric circuit containing a condenser, the terminals of said electric circuit being adapted to be connected with the alternately polarized terminals of said commutator for a period of time greater than the time required to charge the condenser, whereby. the direction of the current in said electric circuit and the charge in said condenser are electrically reversed.

3. Apparatus for producing an alternating current froma direct current, comprising a source of direct current, a commutator the terminals of which are permanently connected to the terminals of said direct current source and an electric circuit c011- taining a condenser, the terminals of said electric circuit being adapted to engage alternately the terminals of said commutator whereby said condenser will be charged and its charge reversed alternately, the timeconstant of said condenser being less than one-half the period of alternation.

REGINALD AUBREY FESSENDEN.

Witnesses:

A. M. GLASS, T. SELBY WARDLE. 

